Camera collars reveal macronutrient balancing in free‐ranging male moose during summer

Abstract Understanding how the nutritional properties of food resources drive foraging choices is important for the management and conservation of wildlife populations. For moose (Alces alces), recent experimental and observational studies during the winter have shown macronutrient balancing between available protein (AP) and highly metabolizable macronutrients (total non‐structural carbohydrates [TNC] and lipids). Here, we combined the use of continuous‐recording camera collars with plant nutrient analyses and forage availability measurements to obtain a detailed insight into the food and nutritional choices of three wild moose in Norway over a 5‐day period in summer. We found that moose derived their macronutrient energy primarily from carbohydrates (74.2%), followed by protein (13.1%), and lipids (12.7%). Diets were dominated by deciduous tree browse (71%). Willows (Salix spp.) were selected for and constituted 51% of the average diet. Moose consumed 25 different food items during the study period of which 9 comprised 95% of the diet. Moose tightly regulated their intake of protein to highly metabolizable macronutrients (AP:TNC + lipids) to a ratio of 1:2.7 (0.37 ± 0.002SD). They did this by feeding on foods that most closely matched the target macronutrient ratio such as Salix spp., or by combining nutritionally imbalanced foods (complementary feeding) in a non‐random manner that minimized deviations from the intake target. The observed patterns of macronutrient balancing aligned well with the findings of winter studies. Differential feeding on nutritionally balanced downy birch (Betula pubescens) leaves versus imbalanced twigs+leaves across moose individuals indicated that macronutrient balancing may occur on as fine a scale as foraging bites on a single plant species. Utilized forages generally met the suggested requirement thresholds for the minerals calcium, phosphorus, copper, molybdenum, and magnesium but tended to be low in sodium. Our findings offer new insights into the foraging behavior of a model species in ungulate nutritional ecology and contribute to informed decision‐making in wildlife and forest management.


FIGURES:
• FIGURES:• Fig. S1 Average proportions of behaviors states across 24h • Fig. S2 Proportions of plants components across diets and forage plants • Fig. S3 Sequences of complementary feeding on imbalanced food items • Fig. S4 (a) Differential birch browsing, (b) RMT of leaves vs. twigs for decid.browse • Fig. S5 Bar plot of sodium (Na) concentrations in vegetation samples • Fig. S6 Scatterplot of copper (Cu) and molybdenum (Mo) concentrations • Fig. S7 Scatterplot of calcium (Ca) and phosphorus (P) concentrations • Fig. S8 Map of Vega Island showing the areas most frequented by moose

Fig. S2
Fig. S2Boxplot showing the dry-matter (DM) proportions of macronutrients (AP: available protein, TNC: total non-structural carbohydrates, TSC: total structural carbohydrates, and lipids) and other plant components in moose diets (as proportionally eaten, blue) and across 25 eaten forages (as if moose had fed on them in random proportions, yellow) on Vega Island (Norway) in July 2022.Significant differences are indicated by asterisks (Welch's t-test, *p < 0.05, **p < 0.01).

Fig. S3
Fig.S3AP:TNC+lipids ratios of consecutive feeding events by three moose (ID1652, ID1764, IDE2808 on Vega Island, Norway July 2022) on nutritionally imbalanced (complementary) food items in relation to the AP:TNC+lipids ratio of the intake target (0.37, red line).

Fig. S5
Fig. S5 Sodium (Na) concentrations as percentage of dry matter (%DM) of 42 potential food items for moose collected on Vega Island, Norway during July 2022.For the items in blue, feeding by moose was observed during the observation period.The dashed vertical line indicates the suggested minimum threshold for sodium (0.1% DM) in ruminant forages.

Fig. S6
Fig. S6 Scatterplot of molybdenum (Mo) and copper (Cu) concentrations in vegetation samples from Vega Island, Norway July 2022 (blue = feeding by moose observed during the study period) with the thresholds for Cu deficiency (dashed horizontal line) and the minimum suggested Cu:Mo ratio (2:1, solid line).

Fig. S7
Fig. S7 Scatterplot of calcium (Ca) and phosphorus (P) concentrations in 42 putative moose forages on Vega Island, Norway in July 2022.The black polygon demarcates the outer hull of the concentrations across all forages whereas the gray polygon indicates the niche realized by moose (i.e., the forages that were eaten; N=25).For the latter, the food items forming the corners of the realized niche are shown in different colors with the size of the circles corresponding to their percentage contribution to the average moose diet.Additionally, Salix (the main food item) is shown in yellow together with the Ca and P concentrations in the average diet (crosshair point).Radials in green indicate the suggested optimal range of the Ca:P ratio for ruminants whereas the dashed red radial indicates the upper threshold.The thin blue lines correspond to the suggested minimum concentrations of Ca and P required by ruminants.

Table S1
The nutritional properties and analytic approach used to study forage plants for moose collected on Vega Island, Norway July 2022.The numbers in square brackets refer to the service package numbers of the DairyOne Forage Laboratory (USA) where the analyses were performed.Detailed methodological descriptions of the chemical analyses used by the laboratory are available at https://dairyone.com/download/forage-forage-lab-analyticalprocedures.Nutritional composition 42 putative moose forages collected on Vega Island (Norway) in July 2022.Values are given as percentages of dry matter (%DM).For items that were consumed by moose during the 5-day observation period, their contributions to average moose diets are given as percentages.For the deciduous forages, the proportions in the diets correspond to twigs and leaves together.

Table S2b
Mineral content of 42 putative moose forages collected on Vega Island (Norway) in July 2022.Values are given as percentages of dry matter (%DM), except for Fe, Zn, Cu, Mn, and Mo, which are given as parts per million (PPM).